The invention relates to an electromagnetic transducer, and more particularly to a magnetoresistive element utilizing a magnetoresistive effect usable for magnetic recorders.
Even as the size of magnetic recorders has decreased and their capacity has increased, the need for an improved; high density magnetic recording technique has increased. The electromagnetic transducer utilizing the magnetoresistive effect (MR effect) is capable of providing a regenerative power, for which reason development of an improved technique utilizing the magnetoresstive effect is essential and important for improvement of high density magnetic recording.
A magnetoresistive transducer or a MR head is disclosed in IEEE Transactions on Magnetics, Vol. MAG-7, No. 1, March 1971 "A Magnetoresistive Readout Transducer". The MR head requires an application of a unidirectional magnetic field onto a magnetoresistive film (Ni--Fe film) for controlling magnetic domains of the film wherein the magnetoresistive film has a magnetic sensitivity to an external magnetic field.
In order to reduce Barkhausen noise, the Ni--Fe magnetoresistive film has a magnetosensensitive film whose opposite ends are laminated thereon with antiferromagnetic films such as Fe--Mn films so that a unidirectional magnetic field is generated due to a switched connection at an interface between the Ni--Fe film and the antiferromagnetic film thereby resulting in the unidirectional magnetic field being applied to the magnetic sensitive portion. This technique is disclosed in the U.S. Pat. No. 4,103,315 issued to Hempstead et al.
According to the technique disclosed in the above U.S. patent, the Ni--Fe magnetoresistive film having the magnetic sensitivity is formed contiguously to the antiferromagnetic film for generating a unidirectional magnetic field for control of the magnetic domains. For that reason, when the antiferrormagnetic film is formed to apply the unidirectional magnetic field to the magnetic sensitive portion of the Ni--Fe film, then the contiguous formation of the Fe--Mn antiferromagnetic film to the Ni--Fe magnetoresistive film results in a magnetization at opposite ends of the magnetic sensitive portion being fixed due to the switched connection between the Fe--Mn antiferromagnetic film to the Ni--Fe magnetoresistive film. The fixed magnetization may degrade sensitivity to the external magnetic field. An outside portion of the Ni--Fe magnetoresistive film positioned outside the magnetic sensitive portion and a soft magnetic film for bias are influenced by a magnetic flux from a track other than the readout track thereby resulting in generation of undesirable noises.
To settle the above problems, the Ni--Fe film is formed only on the magnetic sensitive portion and hard magnetic films are formed at opposite ends of the Ni--Fe film for magnetization thereof to generate the unidirectional magnetic field to thereby apply the magnetic field onto the magnetic sensitive portion. This technique is disclosed in the Japanese laid-open patent application No. 3-125311.
According to the technique disclosed in the Japanese laid-open patent application No. 3-125311, the magnetoresistive film or the bias soft magnetic film resides only on the magnetic resistive portion thereby the device is free from the problem of influences from the magnetic flux from the track other than the readout track. This technique, however, provides the following problem. Due to an actual limitation of an accuracy in alignment in the process for forming a magnetic head or the MR head, electrode films provided at opposite ends of the magnetoresistive film tend to superimpose the opposite end portions thereof so that the actual width of the track is narrower than the predetermined width thereof, resulting in a reduction of the output power.
Under the above circumstances, it has been required to develop a novel magnetoresistive element free from the above problems.